In the 17th century, English dictator Oliver Cromwell sent thousands of Irish into servitude in the Caribbean. For Irishman Denis O'Brien, that history links his country and Caribbean nations like Haiti, founded by black slaves. "There's an affinity there," O'Brien insists.

Even before the Jan. 12 earthquake that wrecked Haiti and killed more than 200,000 people, the phone company O'Brien founded, Digicel, was the nation's largest investor. Since the quake, it has donated and raised $20 million for Haiti, more than any other company so far. Beyond direct aid, O'Brien is also promoting the kind of grass-roots entrepreneurship long ignored by the business elite, which will be critical to Haiti's future. And he's backing reconstruction of Port-au-Prince's Iron Market, a key commercial nexus. "Even if a lot of the Haitian elite don't believe in their country," he says, "I do."
(See photos of American entrepreneurs trying to relieve the ailing residents.)

That Celtic faith in Haiti isn't just O'Brien's. Others in Ireland, including a group of business leaders called the Soul of Haiti Foundation, are building investment and philanthropic relationships with members of a society they feel is capable of rapidly developing its economy the way Ireland has in the past 25 years. Among their beneficiaries: fishermen who got solar panels from Soul of Haiti to make ice that helped them form small seafood-transport companies and farmers who are starting biodiesel firms that use jatropha plants. "Unlike the arrogant cowboy foreign investors you so often meet, they try to learn from us too," says mango exporter Jean-Maurice Buteau. "It's humanitarian, but it's also very down to earth."

Either way, the Haiti work has made O'Brien and the Irish the world's newest poster boys for enterprise-oriented aid of the kind championed by leaders like former U.S. President Bill Clinton, the U.N.'s special envoy to Haiti, and his New York City  based Clinton Global Initiative (CGI). "Denis' efforts on behalf of Haiti redevelopment," Clinton says, "exemplify the CGI model" of joint business, government and civil-society ventures. O'Brien coordinates CGI's Haiti Action Network, which has committed more than $100 million to education, infrastructure and business-development projects  efforts that were bearing fruit when the quake hit.
(See pictures of Haiti's tent cities.)

O'Brien, 52, made his pot of gold (estimated at $3.5 billion) with the 2001 sale of his Irish mobile-phone network, Esat. The son of a human-rights-activist mother then set his sights on the developing world. O'Brien's Jamaica-based Digicel ($2.2 billion in revenue for the year ending March 31) has won almost 11 million subscribers in the Caribbean, Central America and the Pacific by ushering in low prices and more reliable service. It has a 60% market share in Haiti. Before Digicel arrived in 2006, only 5% of Haiti's population used cell phones; today 30% does. "We made Haitian customers feel like New York customers," says O'Brien. One result: the Digicel building in Port-au-Prince was one of the few spared during the 2008 food riots.

Critics in Ireland and the U.K. accuse O'Brien of playing cell-phone populist  "acting the saint in stricken Haiti," as a London Daily Mail article suggested  to deflect attention from a tribunal looking into his financial relationship with the Irish minister who awarded Esat's license in 1996. O'Brien denies any impropriety; he is suing the Daily Mail for libel.
(See pictures of Haiti's gingerbread houses.)

Most Haitians care only that he's acting, period. After the quake, O'Brien gave $5 million to Haitian NGOs; Digicel donated free phone time worth $10 million, as well as cargo planes and boats with relief supplies. It's constructing 50 schools and recently distributed family-size tents to more than 100,000 Haitians.

Yet O'Brien knows that Haiti's long-term recovery is impossible if it doesn't rebuild its entrepreneurial mojo. That's why projects like the 19th century Iron Market, a reminder of a once prosperous Haiti, are among his priorities. As O'Brien and his entourage walk through the market's ruins, navigating rubble, sewage puddles and merchants hawking chickens, the Irishman muses on his affinity for the "raw" surroundings. "It's difficult," he says, "not to get hooked on Haiti."